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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONME1vI, Water Qua[iry Cocrol Division Rationale -Page I1, Permit No. CO-000022! Alternate Limitation Burden of Proof Reouirements: In conformance with 40 CFR 434.63, the permittte has the • burden of proof when requesting relief from rota! suspeMed solids (TSS), total iron andlor settleable solids limitations, as appropriate. The ices of this regulation is to afford relief only when needed due to a volume of water generated by a specific storm went, it is nor icended to be automatically applied to all disdtarges caused by precipitation, nor to be used to discharge volumes in excess ojthat generated by the storm evens. On this basis, relief shall be granted only when necessary and shall not be granted when the permiaee has control over the discharge, enabling them ro meu the primary limitations. The permiaee should endeavor to meu the primary limitations whenever possible. All manual dewatering of ponds that are equipped with automatic dewatering systems mus[ meet TSS and total iron limitations. If a pond has only manual dewarering capability, relief is available only ro the extent required to regain necessary stability and capacity. The Division shall have final authority in determining whether relief is graced. As part of this determination, the Division shall evaluate whether the permittee could have cocro[led the discharge in such a manner that primary limitations could have been met. 1) For rainfall, to waive TSS and total iron limitations, it is necessary to demonstrate that discharge occurred within 48 hours after measurable precipitation has stopped. To waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after precipitation greater than the 10-year, 24-hour eves has stopped. 2) For snowmelt. to waive TSS and rota! iron limitations, it is necessary to demonstrate that discharge occurred within 48 hours afer pond inflow has stopped. To waive senleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after pond inflow volume greater than the 10-year, 24-hour event has stopped. c) Salinity Rerularions: In compliance with section 6.9.2 (12) of the Colorado Discharge Permit Svstem Regulations. the permittee shall monitor far total dissolved solids on a quarterly basis. Samples shall be taken at the effluent discharge poic(s). Salinity requirements are included in Parr I.B.I. e. of the permit. • d) Whole Effluent Toxicirv (WETI Testing: Acute WET testing is required for outfalls 001, 003, 005, 006, 010 and 011; and chronic WET testing is required for ourfatls 004 and 008. See following discztrsian for WET testing for al! of these outfalls. (Also see Parts I.A.4. and I.A.S. of the permit.) 1) Purpose of WET Testinr: The Water Quality Cantro[ Division has established the use of WEI'testing as a method for identifying and cocrolling toxic discharges from wastewater treatmec facilities. WEI'testing is being utilized as a means to ensure that there are na discharges of pollutants "in amounts, concecrarians or combinations which are harmful to the beneficial uses or toxic to humans, animals, plants, or aquatic life" as required by Section 3.1.11 (1) of the Basic Standards and Methodologies for Surface Waters. 2) Instream Waste Concecration (/WC): Where monitoring or limitations for WET are deemed appropriate by the Division, chronic instream dilution as represented ~~ 1he chronic (WC is critical in determining whether acute or chronic conditions shall apply. For those discharges where the chronic /R'C is greater than (>) 9.1 %. chronic conditions apply, where the 1WC is less than or equal to (<_) 9.I acute conditions apply. The chronic /WC is determined using the following equation: /WC = [Facility Flaw (FF)/(Stream Chronic Low Flow (annual) + FF)J X 100`9 Flows and IWC calculations for outfalls 002, 003, 005, 006, 010 and 011 are irrelevant because, in ~ addition to the I1VC value for determining whether chronic or acute WET testing requirements are applicable, the classification ojthe receiving stream must be considered. According to the Colorado Water Oua[iri~ Control Disdsion Biomonitoring Guidance Document. dated July 1, 1993, where the receiving water is classified aquatic life, class 2 without all of the appropriate aquatic life wmeric standards, acute WET resting is required, regardless of dilution. Since the receiving waters for outfalls 002, 003, 005, 006, 010 and 011 are classified as Class 2 Aquatic Life use, but without al! of the appropriate aquatic life numeric . standards, the Division has determined that acute WET testing is applicable for these outfalls (ntso see following paragraph). Since segment 12 is classified this way, outfalls 002, 003, 005, 006, 010 and 011 are subject to acute WET testing requirements.